The invention relates to a device and a method for detecting trace substances in fluid based on synchronized resonance, and belongs to the technical field of sensors. A clamped beam array structure iscomposed of a plurality of clamped beams of the same size and comprises a reference beam and at least one detection beam; two ends of different clamped beams are connected through coupling units, andthe clamped beam array structure and the coupling units are fixed on a support structure; communicated micro-runners are processed inside each clamped beam and the support structure, and the fluid tothe detected sequentially flows through each clamped beam by virtue of a runner inlet in the support structure; an inert material layer is deposited on the micro-runner of the reference beam, and different sensitive layers are deposited on the micro-runners of the detection beams; a piezoelectric disk is arranged at the lower part of the support structure and used for stimulating the array structure to vibrate; and a piezoelectric layer is deposited on the upper surface of each clamped beam and used for enabling the array structure to perform synchronized resonance and detecting signal output. The device provided by the invention has the advantages of being novel in structure, capable of simultaneously detecting multiple substances, and high in resolution.